Image sensors can convert an optical image into an electric signal. With recent developments in the computer industry and the communication industry, there is demand for image sensors with improved performance in various devices such as digital cameras, camcorders, personal communication systems, gaming devices, security cameras, medical microcameras, and robots.
Metal-oxide semiconductor (MOS) image sensors may be easy to drive, and can be driven using various scanning techniques. Also, since signal processors may be integrated into a single chip, it is possible to miniaturize MOS image sensors and reduce the manufacturing cost of MOS image sensors by using a typical MOS processing technique. The power consumption of MOS image sensors is generally low, and, thus, MOS image sensors can be applied to devices with limited battery capacity. For the above-mentioned reasons, the use of MOS image sensors capable of realizing high resolution has dramatically increased.
However, as the integration density of pixels is increased in order to keep up with increasing demand for high resolution, the area of photoelectric conversion elements per unit pixel may be decreased and, thus, sensitivity and saturated signal amount may also decrease. Therefore, active pixel sensor (APS) arrays in which a plurality of photoelectric conversion elements share a read element to maximize the area of light receivers, i.e., the area of photoelectric conversion elements, and thus to increase light-receiving efficiency have been widely adopted.
However, even if a plurality of photoelectric conversion elements share a read element, the read element should read charge accumulated in each of the photoelectric conversion elements. Thus, a plurality of charge-transmission transistors respectively corresponding to the photoelectric conversion elements may need to be turned on or off in response to an additional charge-transmission signal or may need to output charge through additional output lines. In this case, however, the required number of charge-transmission lines or output lines may not be able to be reduced, thereby making it difficult to secure a maximum light-receiving efficiency.